This invention relates to productions of falsetwist textured yarn of polyester filaments, and is more particularly concerned with polyester yarns having a predetermined pattern along the yarn of portions which will dye more deeply than other portions of the yarn.
Conventional processes used for producing polyester textile yarns have involved the steps of melt-spinning polyethylene terephthalate into yarn at take-off speeds of 550 to 1640 yards per minute (500 to 1500 meters/minute) and drawing the as-spun yarn at a draw ratio of about 3.5 to 4.5X to produce fully drawn, uniform yarn. The take-off speed refers to the speed of the solidified as-spun yarn at windup or a roll for forwarding the yarn to subsequent processing. Adams U.S. Pat. No. 3,155, 754 discloses uniform treatment of the as-spun yarn with various liquids for 0.2 second to about 3.0 seconds with immediate removal of the treating liquid, and then drawing the yarn, to make the yarn more receptive to dyes. Suitable liquids are defined as ones which effectively lower the drawing tension when tested by contacting the yarn with the test liquid for one minute, rinsing with water and then immediately drawing the yarn. The patent describes the treated and drawn filaments as having a sheath-core structure in which the core is that of a normal oriented crystalline polyester filament while the sheath, although crystalline, has less orientation than the core and is considerably easier to dye.
Yarn which will dye non-uniformly is frequently desirable to provide an enlivened, variegated appearance in apparel and upholstery fabrics. Werner et al. U.S. Pat. No. 3,478,143 discloses a process of incompletely drawing conventional as-spun yarn to provide a random distribution of thick and thin sections along the filaments. The thick sections are only slightly drawn and dye more deeply than the thin sections, which are substantially fully drawn. The ratio of the average denier or cross-sectional area of the thick sections to that of the thin sections is nearly as large as the draw ratio used (drawn ratios of 2.8X to 3.37X are disclosed in the examples). This amount of denier fluctuation can cause difficulty in processing the yarn into fabric and the fabric is less resistant to abrasion than would be the case with a more uniform yarn. Also, when the yarn is false-twist textured, the thick incompletely-drawn sections melt and fuse together at heater temperatures of over 200.degree. C (needed to obtain good crimp) and fully satisfactory products cannot be made.
Petrille U.S. Pat. No. 3,771,307 discloses that as-spun polyester yarn can be draw-textured on false-twist texturing machines at heater plate temperatures of 227.degree. C when using spin-oriented yarn prepared by melt-spinning at take-off speeds of 3000 to 4000 yards per minute (2744 to 3660 meters/minute). The as-spun yarn is drawn at a draw ratio of 1.3 to 2.0 which is sufficient to provide a fully drawn, uniform yarn. However, the patent does not disclose how to produce polyester yarn having portions which will dye more deeply than other portions.